1. Technical Field
The present invention relates to a method for preparing an alizarin derivative compound, a novel alizarin derivative compound, a surface modification method and surface-modified particles using the alizarin derivative compound, and a photoelectric conversion film, a photoelectric conversion element, and an electrophotographic photoreceptor including the alizarin derivative compound as a component.
2. Background Art
An alizarin derivative compound is a compound which can be applied in a wide range of various fields, such as compounds, complexes, and Lake pigments that are used in organic electronics fields (for example, dye-sensitized solar cells, organic thin film solar cells, organic imaging elements, organic semiconductors, organic EL elements, electrophotographic photoreceptors, and the like), color material fields (for example, inks for inkjet, color copies in a sublimation transfer mode, ink dyes, color filters, silver halide photosensitive materials, printing, optical recording media, colorants for food, and the like), physiologically active materials (for example, anticancer agents, hair growth promoters, and the like), electrolyte solutions, and the like.
As a compound modified at the 4-position, starting from purpurin (a compound represented by the following structural formula), only a few examples have been hitherto reported.

As a method for synthesizing a product obtained by modification of the 4-position of purpurin, for example, a synthesis method shown below is described in Synthesis, 1991, p. 438. In addition, the strength levels of the binding capabilities of the product obtained by modification of the 4-position of purpurin with various metal oxides are discussed using compounds obtained by methylation of the 4-position of purpurin in Angew. Chem. Int. Ed., 2008, vol. 47, p. 10128.

Furthermore, a synthesis method for obtaining a product obtained by modification of the 4-position of purpurin in a short step by protecting a catechol part of purpurin with Ru metal and then introducing an alkyl group thereinto is suggested in Inorg. Chem., 2001, vol. 40, p. 4361.
In addition, there is a report of a modification method for modifying the 4-position of alizarin in a short step by adding a nitro group or bromine to alizarin, then converting the alizarin into an oxidized product, and adding an alcohol thereto (see, for example, J. Chem. Soc., 1962, p. 83, or Ber. Deu. Chem. Gese. B, 1921, vol. 54 B, p. 3035).
Further, as for a novel alizarin derivative compound, isolation by extraction from a natural product/determination of structures/physiological activity (anti-fungus agents), and the like have been found (see Bioorg. Med. Chem. Lett., 2006, vol. 16, p. 4512, Ind. J. Chem., Sec. B (Org. Chem. Med. Chem.), 2004, vol. 44 G, p. 1970, Aus. J. Chem., 1976, vol. 29, p. 2231, Phytochemistry, 1979, vol. 18, p. 906, Acta Mycologica, 1979, vol. 15, p. 183, or Current Science, 1985, vol. 54, p. 998).
There is a demand for a method for synthesizing an alizarin derivative compound formed by using purpurin or the like as a starting raw material and modifying the 4-position of the anthraquinone skeleton in a simple manner and at low cost, but the synthesis methods described in the Non-Patent Documents indicated above suffer from the following problems.
That is, the synthesis method described in Synthesis, 1991, p. 438 not only requires four steps until a desired product is synthesized, but also, it is necessary to use expensive silver oxide in an excessive amount in a third step, resulting in low suitability for production.
Further, according to investigations by the present inventors, it has been confirmed that an alizarin derivative compound (Me-modified product at the 4-position of purpurin) as obtained in Synthesis, 1991, p. 438 returns to purpurin due to deprotection with a MeO group when heated with a Lewis acid, and thus, the stability is threatened in the case of applying the compound in various applications.
In the synthesis method described in Inorg. Chem., 2001, vol. 40, p. 4361, suitability for production is low in view of the use of an expensive metal. Further, in this document, there is no investigation regarding deprotection of a Ru complex part. In addition, in this document, there is only an investigation regarding a methyl-substituted product as a product obtained by modification of the 4-position of purpurin.
In the synthesis method for adding an alcohol through oxidation from nitroalizarin as described in J. Chem. Soc., 1962, p. 83, the 4-position of alizarin can be modified in a short step, but the resulting modified product has low stability. Further, as for a synthesis method, there is risk involved due to the coexistence of an oxidant and an alcohol, and thus its suitability for production is low.
In the method for addition of an alcohol through oxidation involving addition of bromine from alizarin as described in Ber. Deu. Chem. Gese. B, 1921, vol. 54B, p. 3035, the 4-position of alizarin can be modified in a short step, but a desired compound is not necessarily obtained by adding bromine, and further, it easily becomes a complex mixture. According to practical investigations by the present inventors, additional testing has been impossible.
Furthermore, in the methods described in Bioorg. Med. Chem. Lett., 2006, vol. 16, p. 4512, Ind. J. Chem., Sec. B (Org. Chem. Med. Chem.), 2004, vol. 44G, p. 1970, Aus. J. Chem., 1976, vol. 29, p. 2231, Phytochemistry, 1979, vol. 18, p. 906, Acta Mycologica, 1979, vol. 15, p. 183, and Current Science, 1985, vol. 54, p. 998, suitability for production is also low.
Moreover, in the case of using purpurin as a raw material, purpurin which is available as a commercial product (for example, products manufactured by Tokyo Chemical Industry Co., Ltd. and Kanto Chemical Co., Ltd. are available) contains quinizarin (a compound having the following structure) as an impurity in an amount of about 15%. According to the investigations by the present inventors, it has been proven that if such purpurin is used as a raw material in the above-described synthesis method, a large degree of loss is involved in the separation of quinizarin, thereby resulting in even lower suitability for production.

On the other hand, from the viewpoint that an alizarin derivative compound such as a product obtained by modification of the 4-position of purpurin, or the like can modify the surface of an inorganic compound solid material such as a metal oxide or the like using the coordination bond with the surface, there is a demand for a compound which has various substituents introduced to the 4-position of purpurin and stably forms a complex with the metal oxide in order to adjust the physical properties of the surface of the inorganic compound solid material while not weakening the coordination capability, and a method for preparing the same, which have hitherto not been provided.